The field of candidates to run the Securities and Exchange Commission is shifting after a contender dropped out of the race.

Mary J. Miller, a senior Treasury Department official, removed her name from consideration in recent days, according to several people briefed on the matter who were not authorized to discuss the selection process. While some Washington insiders had considered Ms. Miller a sensible choice, several people close to her said she was “not interested” in the job.

With Ms. Miller withdrawing, Sallie L. Krawcheck, a longtime Wall Street executive, has emerged as a potential front-runner. Over the last year, she has become a familiar face in Washington, making the rounds with lawmakers to discuss consumer issues.

The White House, which has been holding interviews for the position in recent weeks, is vetting a number of candidates with backgrounds in finance and government.

Robert S. Khuzami, the S.E.C.’s enforcement director, is favored by some agency officials. Richard G. Ketchum, chairman and chief executive of the Financial Industry Regulatory Authority, Wall Street’s internal policing organization, is also a long-shot contender. The search is still in its early stages, and the candidates could change as the White House narrows its choices.

Washington and Wall Street have been abuzz with speculation about the next S.E.C. chief since Mary L. Schapiro, the current chairwoman, announced her resignation on Monday. President Obama quickly named Elisse B. Walter, a Democrat who became an S.E.C. commissioner in 2008, as the new chief of the agency.

But while Ms. Walter will step into the role on a full-time basis, she has told agency officials that she plans to serve for a short time. The White House, which faces more pressing cabinet-level nominations, is expected to name an S.E.C. successor next year.

The president’s choice for the job will send a strong message to Wall Street and the broader financial markets. He could select a candidate with a strong regulatory hand and a critical voice to help police the industry.

Or the Obama administration could decide on a compromise candidate like Ms. Krawcheck. In addition to having extensive Wall Street credentials, she is known for her independent streak and consumer advocacy efforts.

Since leaving Bank of America in late 2011, Ms. Krawcheck, 48, has stepped up her presence in Washington and even hired an aide to help her navigate the political arena, according to people briefed on the matter who spoke on condition of anonymity.

Last week, she met with leading members of the Senate Banking Committee, which oversees the S.E.C. It is possible Ms. Krawcheck is being considered for jobs other than head of the S.E.C., these people said.

Still, she lacks government experience. Her banking résumé, too, may prove problematic given the anger of many people in Washington and on Main Street over Wall Street’s role in the 2008 financial crisis.

Some liberal lawmakers are expected to raise concerns that regulators, including the S.E.C., are taking aim at some of Ms. Krawcheck’s past employers. She has been personally named, along with former colleagues, in litigation stemming from her time at Bank of America and Citigroup.

Ms. Krawcheck started on Wall Street as an investment banker at Salomon Brothers, and switched a few years later to Donaldson, Lufkin & Jenrette. She made a name for herself as an analyst at Sanford C. Bernstein, a research firm, where she covered the banking industry and often issued negative calls on firms like Citigroup. In 2001, she was named chief executive of Bernstein, making her one of the top women on Wall Street.

A year later, during a scandal on Wall Street, she was hired as head of research and brokerage at Citigroup, a step the bank took to improve its credibility. She worked her way up at Citigroup, becoming chief financial officer and eventually head of the wealth management division. But she left the bank in September 2008 after clashing with top executives who were reluctant to reimburse clients who had lost money on certain Citigroup investments.

In 2009, Ms. Krawcheck landed at Bank of America, where she ran the wealth management group. Under her leadership, the unit posted steady results, a point of strength for the then-troubled bank. But Ms. Krawcheck was ousted from Bank of America in 2011 as part of a broader management shake-up.

Since then, Ms. Krawcheck has refined her voice as a consumer advocate. On Twitter, she has drawn a significant following with her conversational style and posts on investment issues. She is on the board of Motif Investing, an online brokerage firm geared toward individual investors.

She also writes a blog on LinkedIn. One recent dispatch, titled “What I Learned When I Got Fired (The First Time),” offered career guidance from her own rocky periods.

“If you haven’t been fired at least once, you’re not trying hard enough,” she wrote. “As the pace of change in business increases, the chances of having a placid career are receding. And if in this period of rapid change, you’re not making some notable mistakes along the way, you’re certainly not taking enough business and career chances.”

The next head of the S.E.C. faces a challenging agenda.

Ms. Schapiro, who stepped down after a difficult four-year run, overhauled the agency and brought it back from the brink. During her tenure, she revamped the enforcement division and replaced the leadership team.

But the new chief will have to tackle high-speed trading and complex financial products that have proved tough to monitor. At the same time, the S.E.C. must play catch-up on a series of rule-writing efforts required under the Dodd-Frank Act, the sweeping regulatory overhaul passed after the financial crisis. The agency is also trying to safeguard its rules from Wall Street’s legal challenges.

“It’s still a very daunting task,” said Barbara Roper, director of investor protection at the Consumer Federation of America, an advocacy group.

A version of this article appears in print on 11/29/2012, on page B1 of the NewYork edition with the headline: As Official Drops Out, Race Shifts For S.E.C..